The present invention relates to a needle actuation device for knitting machines for hosiery or other articles.
It is known that knitting machines for hosiery or other articles are generally constituted by a needle holder, which can be substantially flat and straight or cylindrical, depending on whether the machine is of the rectilinear or circular type, and faces a cam box which supports a plurality of cams for actuating the needles during the operation of the machine.
More particularly, on the face of the needle holder that faces the cam box a plurality of mutually parallel slots are provided, each of which accommodates a needle and optionally a needle pusher. The needles, and optionally the needle pushers, are provided with heels which protrude from the needle holder toward the cam box so as to engage in paths defined by the cams. The needle holder, during the operation of the machine, is actuated along a direction of motion with respect to the cam box so that the heels of the needles or of the needle pushers engage in said paths, which have portions that are appropriately inclined with respect to the direction of motion in order to produce a reciprocating motion of the needles along the corresponding slots of the needle holder. This reciprocating movement causes the needles to take up the yarns supplied at one feed of the machine and form loops of knitting.
The cam that determines the movement of the needle, after the needle has engaged the yarn at a feed of the machine is termed lowering cam, since it causes a movement of the needle that forms a new loop of knitting, lowering the previously formed loop of knitting.
The lowering cam has a profile that can be engaged by the heels of the needles or of the needle pushers and is inclined with respect to the direction of motion of the needle holder with respect to the cam box indeed in order to achieve this movement of the needle.
In single-cylinder circular knitting machines for hosiery or other articles, in which the needle holder is constituted by the needle cylinder, the lowering cam, arranged directly after a feed or drop of the machine, causes the descent of the needles inside the slots formed on the lateral surface of the needle cylinder after said needles have engaged the yarn at the drop or feed.
In many kinds of knitting machine for hosiery or other articles, the lowering cam is mounted on a slider that can move on command, with respect to the cam box, along a direction that is parallel to the extension of the slots that accommodate the needles, so as to allow to vary the extent of the motion of the needles during the formation of new loops of knitting and therefore allow to vary the length of the loops of knitting.
In other kinds of machine, the lowering cam is fixed to the cam box, and the length of the loops of knitting is changed by moving the needle holder with respect to the cam box in a direction that is parallel to the extension of the slots that contain the needles.
The profile of the lowering cams currently used in knitting machines for hosiery or other articles has a relatively high inclination with respect to the direction of the motion of the needle holder relative to the cam box. This high inclination is necessary because during the formation of very long loops of knitting the yarn must rest on a small number of sinkers or regions of the needle holder in order to reduce the friction that contrasts the sliding of the yarn during the formation of the new loops. Said friction, if excessively high, might lead to the breaking of the yarn or to stretching of the loops formed previously on the same row of knitting. This high inclination, which is necessary in the knitting of long loops, prevents any increase in the operating speed of the machine, since it would cause rapid wear of the lowering cam and of the heels and might even break the heels of the needles or of the needle pushers.
In order to allow to increase the operating speed of the machine at least during the knitting of short loops, a device has been proposed which is the subject of U.S. Pat. No. 6,164,090 by the same Applicant and in which the lowering cam can rotate about an axis that is perpendicular to the surface of the portion of the needle holder that in each instance faces the cam box, so as to be able to vary the inclination of the profile of the lowering cam with respect to the direction of the motion of the needle holder with respect to the cam box.
This patent further provides for the possibility to obtain an automatic variation, particularly a reduction, of the inclination of the profile of the lowering cam when the lowering cam is moved with respect to the cam box in order to vary the length of the loops of knitting, particularly in order to reduce their length.
In the above cited patent, this automatic variation is obtained following a particular coupling of the lowering cam with the cam box and inevitably renders the inclination of the profile of the lowering cam dependent on the is length of the loops of knitting.
The aim of the present invention is to provide a needle actuation device for knitting machines for hosiery or other articles that allows, according to requirements, to vary the inclination of the profile of the lowering cam both in a manner that is correlated to the variation of the length of the loops of knitting and in a manner that is independent of the variation of the length of the loops of knitting.
Within this aim, an object of the invention is to provide a device that is structurally simple and can be fitted on a wide range of knitting machines for hosiery or other articles.
This aim and these and other objects that will become better apparent hereinafter are achieved by a needle actuation device for knitting machines for hosiery or other articles, comprising a cam box which faces a needle holder and supports at least one lowering cam whose profile is inclined with respect to the direction of the motion of said needle holder with respect to said cam box; said profile of the lowering cam being engageable by a heel of the needles or of needle pushers which protrudes from said needle holder toward said cam box; said needle holder having, on its face that faces said cam box, a plurality of slots that are parallel to each other and lie substantially at right angles to said direction of motion, each slot accommodating a needle that can slide along the corresponding slot; said lowering cam profile being suitable to produce a movement of the needles along the corresponding slot of the needle holder after engaging the yarn at a feed of the machine, in order to form new loops of knitting, lowering the previously formed loops of knitting, said lowering cam being supported by said cam box so that it can rotate about a rotation axis that is substantially perpendicular to the surface of the portion of said needle holder that in each instance faces said cam box, characterized in that it comprises first means for adjusting the position of said lowering cam with respect to said needle holder along an adjustment direction in which at least one component is parallel to the direction of the sliding of the needles that in each instance engage said lowering cam along the corresponding slots of the needle holder, in order to vary the length of the loops of knitting, and, means for connecting a portion of said lowering cam that is spaced from said rotation axis to said cam box for a rotation of said lowering cam about said rotation axis with respect to said cam box as a consequence of the translational motion of said lowering cam along said adjustment direction with respect to said cam box; second adjustment means being provided which are connected to said lowering cam and can be actuated for a rotation of said lowering cam about said rotation axis with respect to said cam box, independently of the translational motion of said lowering cam along said adjustment direction with respect to said cam box.